PART I,] Varying Prevalence of Cholera in Calcutta. 209 



Some other returns which were also manifestly incorrect we have been able in some 

 degree to rectify, especially such of them as presented inverse reading of the fluctua- 

 tions of the water-level. These have been marked with an asterisk in the tables. It 

 will be observed, also, that at some of the stations observations have been made 

 only during very short periods. These have, however, been put on record, as they 

 may, perchance, be of use to future observers in studying localised outbreaks of 

 disease that may occur at those particular stations. 



In the water-level returns for Calcutta, the monthly mean of the daily returns 

 has been calculated for all the years ; but with regard to the others, the observation 

 recorded in the middle of each month has been taken as offering sufficiently precise 

 information. 



It was our intention to have analysed the records obtained from Madras and 

 Bombay on the present occasion also, but we found that the task was more than 

 could be accomplished satisfactorily at present. On a future occasion we hope to 

 deal with these also, and to do so, if practicable, not only in connection with the 

 question of cholera, but also with relation to the prevalence of malarial fevers 

 and dysentery. 



I.— CHOLEEA IN CALCUTTA. 



CHAPTEE I. 



THE SEASONAL FLUCTUATIONS IN THE PREVALENCE OF CHOLERA IN AN ENDEMIC AREA- 

 CALCUTTA. 



Of all regions where the nature of the influence of seasonal conditions on the prevalence 

 of cholera can be enquired into, the endemic area of the disease, and more especially the 

 endemic area as represented by the lower portion of the Grangetic delta, is perhaps the 

 best adapted to the end in view. In it the constant presence of the disease and the 

 regularity with which the phenomena of fluctuations in its prevalence occur furnish 

 data which are more readily comparable with those of a physical nature than can be 

 obtained in regions where cholera only occurs occasionally and in epidemic outbursts. 

 The data regarding a typical locality in this area — Calcutta — have therefore been gone 

 into at considerable length and in greater detail than has been attempted in reference 

 to other places ; but regarding almost all the localities considered in the report, sufficient 

 data are supplied to allow of their comparison with Calcutta in most important respects. 



Our data regarding the varying prevalence of cholera in Calcutta at different times 

 of year are mainly derived from three sources — liSt, the table published by Dr. John 



